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Sydney University scientists work on the Large Hadron Collider

Scientists from the University of Sydney's High Energy Physics group have been playing a key part in the world's biggest and most expensive scientific experiment - the Large Hadron Collider.

The ATLAS detector in the Large Hadron Collider has a team of University of Sydney scientists working on it.

The Large Hadron Collider, which made international headlines when it started on 10 September, is the world's largest and most powerful particle accelerator, which will provide significant insights into the origins of the universe including the mysterious 'dark matter' that occupies much of space.

With protons smashing together at nearly the speed of light, the Large Hadron Collider has a number of particle detectors to record what happens at each collision.

University of Sydney scientists, along with colleagues at the University of Melbourne, are working on one of the two main detectors on the Large Hadron Collider, called ATLAS (A Toroidal LHC ApparatuS).

There are six detectors on the Large Hadron Collider, with ATLAS and CMS being the two largest general-purpose detectors responsible for analysing the myriad of particles produced by the collisions in the accelerator.

Staff members in the University of Sydney's High Energy Physics group: Dr Kevin Varvell, Dr Bruce Yabsley and Dr Aldo Saavedra, plus their PhD students Jason Lee and Anthony Waugh, have been involved in testing and developing the units that measure the position of charged particles as they travel through ATLAS, plus the software that analyses the data from ATLAS.

"With a length of 46 metres, a height of 25 metres, a width of 25 metres, and weighing 7 000 tonnes, ATLAS is the largest volume particle detector ever constructed at an accelerator," said Dr Kevin Varvell.

"ATLAS is designed to investigate the largest range of physics possible by recording measurements on the particles created in the collisions - their paths, energies, and their identities," explained Dr Varvell.

Dr Aldo Saavedra said of the Australian involvement, "We were involved in the large research and development effort directed at creating the components of the ATLAS detector in the early stages of the experiment. Australia, through Sydney and Melbourne Universities, was involved in testing and developing the strip detectors that are mounted in layers around the collision to recreate the path of the charged particles made in the collision."

"Now that the detector is built, our focus has been contributing to the software that analyses the data from ATLAS. It has been said that if all the data from ATLAS was recorded, it would fill 100 000 CDs per second. In reality, this is cut down to 27 CDs-worth per minute to keep it reasonable by the ATLAS trigger," said Dr Saavedra.

"One of our current projects is to decrease the amount of data saved by increasing the efficiency of capturing the interesting information - the bits that may contain a new discovery.

"There are lots of ways to trigger the detector to save the data. In Sydney, our interest is triggering with the tau lepton, which is a heavy cousin of the electron. Being heavy has two advantages: it produces a striking signature in the detector and it means that we would often expect tau particles to turn up as the decay products of the particles we want to discover," explained Dr Saavedra.

Students who get the chance to work on ATLAS have an amazing opportunity to make their mark in the world of particle physics.

Jason Lee and Anthony Waugh, PhD students in the University of Sydney's High Energy Physics group, are working on reconstructing and identifying the different particles recorded by ATLAS and finding ways to more efficiently model the detector in order to understand how it will respond.

Anthony Waugh said, "ATLAS is a great project to work on. The opportunity to collaborate with some of the leading physicists in the world, on the largest experiment in the world, is very exciting. The biggest thing is knowing that although the Australian group is small in numbers, our contribution has been and will continue to be, extremely important and genuinely valued by the ATLAS community."

Australia has invested approximately $2.5 million in the ATLAS project. Australian scientists join more than 2 500 scientists from 169 institutes in 37 countries working on ATLAS, making it one of the largest collaborative efforts ever attempted in the physical sciences.

Part of the public interest in the Large Hadron Collider has been driven by claims that the experiment will end the world.

Dr Bruce Yabsley said, "Some people have raised safety concerns about the Large Hadron Collider, because it's new and the highest-energy collider we've ever built. But, in fact, the proton-beam collisions in ATLAS and the other detectors are at low energies in the wider scheme of things.

"Cosmic rays hitting Earth's atmosphere, or the moon, can reach much higher energies; and even those energies are dwarfed by cosmic ray collisions in space. All of these things have been going on for billions of years.

"We can't compete with nature on energy, and we're not trying to: the point of the Large Hadron Collider is to access some of these interactions in the lab - inside these big and precisely instrumented detectors - where we can study them properly," explained Dr Yabsley.

History: other Sydney University scientists involved in ATLAS

In addition to the current University of Sydney team working on ATLAS, there have been others who worked on the project:

* Honorary Associate Professor Lawrence Peak steered the University of Sydney group through the earlier days of their ATLAS involvement in the mid 1990s. Since retiring, he continues to be involved as an Honorary Associate Professor of the School of Physics and still holds ARC grants, including one with Dr Kevin Varvell.

* Honorary Senior Lecturer Juris Ulrichs helped the University of Sydney group through the process of organising a tender for production of several large copper alloy shields for ATLAS several years ago. The University of Sydney managed the tendering process and a Western Australian company, VEEM Engineering, won the contract. He has since retired.

* Dr Grant Gorfine worked as a postdoctoral researcher with the University of Sydney group for several years on ATLAS. He has continued to work on ATLAS, now employed by European groups and based at CERN.